A portable electrical power tool has a housing in which a motor serving as a drive source is accommodated, and an L-shaped battery pack serving as a power source for driving the motor is assembled to one end of the housing. Energization and de-energization of the motor and acceleration and deceleration of the motor are performed upon operation of a switch assembly.
Japanese Patent Application Kokai No. H09-011141 discloses an angled impact driver which is one of the examples of the portable electrical power tool. The angled impact driver generates impulse rotation force upon rotation of the motor so as to impactingly rotate an end bit about its axis for facilitating a screw fastening operation. The angled impact driver provides lesser reaction force with increased fastening performance, and is particularly available for screw fastening work at a narrow working site.
Relevant conventional angled impact driver 101, 201 are shown in FIGS. 4 and 5 in which a motor 103, 203 is accommodated in a housing 105, 205 at a longitudinally center portion thereof. The housing 105, 205 also accommodates therein, at a front side of the motor 103, 203 (right side in FIGS. 4 and 5), a planetary gear deceleration mechanism 106, 206, an impulse rotation mechanism, and a bevel gears 107,108 and 207, 208. The impulse rotation mechanism includes a spindle 110, 210, a hammer 111, 211, an anvil 104, 204, a cam mechanism, a ball 112, 212, and a spring 113, 213. An L-shaped battery pack 102, 202 is detachably attached to an end portion of the housing 105, 205. A switch assembly 119, 219 provides speed changing function and includes a switch body 120, 220 and a trigger 121, 221.
In the angled impact driver 101 shown in FIG. 4, the switch body 120 and a trigger 121 are disposed between the motor 103 and the L-shaped battery pack 102. Upon pulling the trigger 121, electrical power is supplied from the L-shaped battery 102 to the motor 103 to energize the motor 103. Further, rotation speed of the motor 103 can be changed in accordance with an amount of pulling of the trigger 121.
In the angled impact driver 201 shown in FIG. 5, the switch body 220 and the trigger 221 are disposed also between the motor 203 and the L-shaped battery pack 202. The trigger 221 is of a paddle type whose fulcrum end 222 is positioned below the switch body 220. The trigger 221 has a manipulation portion 221a elongating frontward from the fulcrum end 222 so that the manipulation portion 221a can be positioned at a center of gravity of an entire impact driver.
With this structure, an entire length of the driver 101, 201 is disadvantageously long, since the switch body 120, 220 is disposed between the motor 103, 203 and the L-shaped battery pack 102, 202. Further, in the driver 101 shown in FIG. 4, poor operability may result, since the position of the trigger 121 is not coincident with the center of gravity of the entire impact driver. In the driver 201 shown in FIG. 5, the manipulation portion 221a is frontwardly away from the fulcrum end 222. Therefore, the manipulation portion 221a is spaced away from a tool gripping portion, thereby lowering operability.